1. Field of the Invention
Technical Field
The present invention generally relates to vacuum technology, and more particularly, to a cryopump control apparatus, a cryopump system, and a method for evaluating vacuum retention of cryopumps.
2. Description of the Related Art
Background Art
A cryopump is a vacuum pump that attains a clean high vacuum environment, and is utilized, for example, to maintain a high vacuum in a vacuum chamber used in a semiconductor circuit manufacturing process. A cryopump accumulates gas by condensing or adsorbing gas molecules on cryopanels cooled to an ultra cold temperature by a refrigerator so as to exhaust gas from a vacuum chamber.
If cryopanels are covered by gases that have been condensed and converted to solid state, or if adsorbents of the cryopump have adsorbed gases almost to its maximum adsorption capacity, the pumping capability of the cryopump decreases. Thus, a regeneration process is executed, as appropriate. In the regeneration process, first the temperature of cryopanels is raised so that the accumulated gases are liquefied or evaporated and discharged, accordingly. Next the cryopump is evacuated and then whether the vacuum is maintained properly (i.e., vacuum retention state) is evaluated. Thereafter, the cryopanels are cooled to an ultra cold temperature so that the cryopump can be used again.